Scientists recently developed a
new modeling approach to estimate sea ice thickness. This is the only model
based entirely on historical observations.

The
model was developed by scientists with the U.S. Geological Survey and the Russian Academy
of Sciences, Moscow.

Using this
new technique, the thickness of Arctic sea ice was estimated from 1982 to 2003.
Results showed that average ice thickness and total ice volume fluctuated
together during the early study period, peaking in the late 1980s and then declining
until the mid-1990s. Thereafter, ice thickness slightly increased but the total
volume of sea ice did not increase.

Scientists
propose that the volume stayed constant during the study's latter years because
while the ice was thickening in the high latitudes of the Arctic,
the surrounding sea ice was melting. Sea ice, however, can only become so thick,
and if Arctic sea ice continues to melt, the total volume of sea ice in the Arctic will decrease.

The
most dramatic losses in sea ice cover have occurred since 2003, and as
scientists acquire newer data, they will apply the new model to study recent
years of ice thickness and volume change.

This modeling approach uses sea
ice motion data to follow parcels of ice backward in time at monthly intervals for
up to 3 years while accumulating a history of the solar radiation and air temperature
to which the ice was exposed. The model was constructed by fitting these data
with an ice parcel's known thickness to determine how the thickness of sea ice changes
in response to different environmental conditions. Data on the known thickness are
obtained from measurements by submarine cruises and surface coring missions.

"Sea
ice is affected by the accumulation of environmental factors to which it has
been exposed," said USGS Director Mark Myers. "Understanding the natural
variability of sea ice thickness is critical for improving global climate
models. Sea ice regulates energy exchange and plays
an important role in the Earth's climate system."

This model,
built on historical observations, complements thermodynamic models that simulate
ice thickness. Science benefits from having different models. Comparing
different model outputs can help improve predictive capabilities. Many
scientists worldwide are using satellite and ground observations of the Arctic's atmosphere, ice and ocean to gain a better
understanding of how changes at the top of the world affect ecosystems both
locally and globally.

The report "Fluctuating Arctic sea
ice thickness changes estimated by an in-situ learned and empirically forced
neural network model" was recently published in the Journal of Climate and can
be found at the American
Meteorological Society's journal site.